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The City of Sweetwater, Texas, (population 12,000) shut down their surface water treatmentplant in December, 2001. Originally constructed in the 1920s, the conventional treatment plant(rapid mix - flocculation - sedimentation - filtration) could not meet the finished water turbidityrequirements that became effective January 1, 2002. Additionally, monitoring at the plantconducted prior to shutdown revealed an inability to meet a 25% reduction in total organiccarbon (TOC) as required under provisions of the Interim Enhanced Surface Water TreatmentRules also effective for Sweetwater on January 1, 2002.Planning for the future, the City of Sweetwater conducted pilot studies from October, 1999,through March, 2000, to test the treatment capabilities of membrane technologies. Pilotobjectives included:demonstrating organic removal performance;demonstrating turbidity/particle removal capabilities;demonstrating the overall treatment capability for feed water from three surfacewater sources; and,determining the design and operating parameters for a full-scale plant.The size of natural organic matter present in surface waters is smaller than the pore size ofmembranes. The pilot study focused on optimizing TOC removal by enhanced coagulationupstream of the membranes. The goal was to generate pin-sized floc particles large enough tobe removed by ultrafiltration. The ZeeWeed Immersed Membrane System from ZENONEnvironmental Systems, Inc. met all of the study objectives.TOC reductions of over 32% were achieved when the ZENON pilot unit was operated forenhanced coagulation. Design parameters developed from the pilot study included provisionsfor rapid mixing of the coagulant, followed by a limited flocculation stage of 12.5 minutes prior toentering the membrane tanks. By controlling system recovery and maintaining a high solidsconcentration in the membrane process tanks, TOC reductions meeting or exceeding theregulatory standards will be achievable in the full-scale plant.The City of Sweetwater's new 8.0 MGD (30.28 MLD) surface water treatment plant is underconstruction, with startup anticipated in August 2003. In addition to combining enhancedcoagulation for TOC removal with ultrafiltration, design of the full-scale plant includes asecondary UF process tank to achieve a 99% recovery of feed water. These two designcharacteristics (enhanced coagulation and 99% recovery) are key elements of the firstimmersed, vacuum-driven membrane system in Texas. Includes 6 references, tables, figures.

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Edition: Vol. - No. Published: 03/05/2003 Number of Pages: 18File Size: 1 file , 430 KB